Cannibal Star Gobbles Up Companion and Starts Acting Younger

Data from NASA's Chandra X-ray Observatory show new evidence of a "cannibal" star that recently devoured its companion star or planet, possibly also spawning a second generation of exoplanets in the process.The composite image on the left shows X-ray and optical data for BP Piscium (BP Psc), a more evolved version of our sun, located about 1,000 light-years from Earth.Credit: X-ray (NASA/CXC/RIT/J.Kastner et al), Optical (UCO/Lick/STScI/M.Perrin et al); Illustration: NASA/CXC/M.Weiss [Full Story]

Space can be
a pretty rough place, and it just got rougher. A study has found evidence of a "cannibal
star" that recently devoured a companion star or planet, possibly spawning
a second generation of exoplanets in the process.

Data from
NASA's Chandra X-ray Observatory showed that the star, called BP Piscium (BP
Psc), is a more-evolved version of our sun, but with a surrounding disk of dust
and gas usually associated with young stars.

Such disks are thought to give
rise to planets. Because BP Psc is relatively aged, the disk is somewhat of a
mystery. [Image of the cannibal star]

Optical data
also revealed a pair of
jets, several light-years long, extending from the poles of the star and shooting
material at high velocities out of the system in opposite directions. These
jets, too, are typical of a very young star.

Normally, a
young star grows bigger as debris from the surrounding disk falls onto it. The
star incorporates about 90 percent of the dusty, gaseous material and recycles
the remainder through its jets.

Not what
it seems

To explain
the presence of young-star features on the elderly star, scientists suggested
that BP Psc appropriated the disk and jets from a younger neighbor that it
gobbled up.

"It
appears that BP Psc represents a star-eat-star universe, or maybe a
star-eat-planet one," said the study's leader, Joel Kastner, a professor
at the Rochester Institute of Technology. "Either way, it just shows it's
not always friendly out there."

BP Psc is
located about 1,000 light-years from Earth, in the constellation Pisces. The
star, including its disk and jets, is about two light-years wide.

Piecing
it all together

The disk and
jets may disguise BP Psc's true age, but other characteristics of the star are giveaways.
Most young stars form in clusters. BP Psc, by contrast, is isolated and not
located near any star-forming cloud. Furthermore, its surface gravity appears
to be weaker than would be expected for a young star. And its atmosphere
contains only a small amount of lithium, as do the atmospheres of most elderly
stars.

Chandra's X-ray eyes provided additional evidence. Young,
low-mass stars are brighter than most other stars in the X-ray spectrum, and Chandra's
examination of BP Psc revealed that its X-rays are too low to be from a young
star. The detected X-ray emission rate is more consistent with those of rapidly
rotating giant stars.?

"It
seems that BP Psc has been energized by its meal," said study co-author Rodolfo
Montez Jr., also from the Rochester Institute of Technology.?

Unmasking
BP Psc

BP Psc is
not too different from what scientists expect of our sun toward the end of its
life. ?When the sun becomes a red giant star like BP Psc, it will swell so much
that it may even consume Earth.

"BP Psc
shows us that stars like our sun may live quietly for billions of years, but
when they go, they just might take a star or planet or two with them,"
said study co-author David Rodriguez, from UCLA.

At the
moment, the researchers are unsure whether it was a companion star or a planet
that BP Psc gobbled.

"It could be
a small star or a large planet," Kastner said. "We don?t know which it could
be, but we?re very interested in finding out."

Not all
is lost

Even if BP
Psc is killing off some of its planets, it also could be spawning replacements,
evidence suggests.

?A second round
of exoplanets may be growing from the star's disk, hundreds of millions of
years after the first round of planetary formation, scientists say.

A separate
study that used observations from NASA's Spitzer Space Telescope reports possible evidence of a giant
planet in BP Psc's orbiting disk. This could be either a newly formed planet or
one that was part of the star's original planetary system.

"Exactly
how stars might engulf other stars or planets is a hot topic in astrophysics
today," Kastner said. "We have many important details that we still
need to work out, so objects like BP Psc are really exciting to find."

Studying
these so-called cannibal stars could also aid the search for new planets beyond
the ones in our own solar system.

"In
order to understand the extrasolar planets that are now being discovered by the
dozen, we need to figure out how planets might be forming, and therefore where
we should go look for them," Kastner said. "I think this object is
especially interesting because it gives us a good shot at finding young planets
around an old star."

The results
of the study are detailed in a recent issue of The Astrophysical Journal
Letters.